Air baffle apparatus



1970 I R. 'M. OEHLSCHLAEGER 3,

AIR BAFFLE APPARATUS 3 Sheets-Sheet 2 Filed April 24, 1968 FIG. 4.

A l I INVENTOR BY R! CHARD M. OEHLSCH LAEGER ATTYS Jan. 20, 1970 R. M. OEHLSCHLAEGER 3,490,352

AIR BAFFLE APPARATUS Filed April 24, 1968 3 Sheets-Sheet s WIND DIRECTION THERMAL EFFICIENCY, PERCENT O 5 l0 15 2O 25 3O WIND VELOClTY,MlLES/HOUR RICHARD M. OEHLSCHLAEGER INVENTOR:

ATT YS.

United States Patent 3,490,352 AIR BAFFLE APPARATUS Richard M. ()ehlschlaeger, Novelty, Ohio, assignor to American Gas Association, Inc,, New York, N.Y., a

corporation of New York Filed Apr. 24, 1968, Ser. No. 723,731 Int. Cl. E04f 17/02 US. Cl. 98-58 13 Claims ABSTRACT OF THE DISCLOSURE Air baflle apparatus for reducing the effects of wind on the supply of combustion air to a roof-top gas burner of the type in which combustion air is drawn into the burner through a horizontal inlet opening communcating with the atmosphere and vent gases are vented through a pipe extending outwardly and upwardly through the center of said opening. A horizontal top surface is provided around the inlet opening, and a frustoconical hood is aflixed to the exterior of the vent pipe above the top surface. The hood has downwardly sloping sides which extend beyond the outer edges of the inlet opening, and which are provided with a horizontal ring of holes. A deflecting baflle in the form of an annular metal strip extends around the interior of the hood in the plane of the ring of holes, in a position and at an angle to deflect downwardly and backwardly that air which passes through the holes in response to wind, thereby to counteract the tendency for wind to increase the flow of combustion air along the top surface beneath the hood and into the inlet opening.

BACKGROUND OF THE INVENTION This invention relates to air bafile apparatus for reducing the effects of wind on air flow through an orifice, and to systems employing same.

There are a variety of applications in which an orifice communicates with atmosphere in a position subject to the influence of wind, and in which it is desirable that the flow of air through the orifice be affected as little as possible by the magnitude of the wind. One example of such an application arises in connection with so-called sealed-combustion gas-fired heaters, in which the combustion air for combustion of the gas flame is provided, not directly from the ambient atmosphere, but by way of a supply conduit having an orifice communicating with atmosphere. For example, a gas-fired heater within a building may be supplied with combustion air through a conduit leading to the exterior of the building, and vent gases from the heater may be delivered to the exterior through another conduit. In another form of apparatus, with respect to which the invention is hereinafter described in detail, a so-called roof-top heater is employed which contains a gas burner supplied with combustion air through an orifice communicating with atmosphere, the heater being used, for example, to heat air or water which is circulated into the building below. Because the combustion-air inlet orifice communicates with the atmosphere, it is susceptible to the influence of winds tending to change markedly the flow of combustion air, often resulting in lowered thermal efficiency at the heater, outage of the pilot flame, and/ or instability of the heater flame.

While it is known in the prior art to provide various types of air bafile means adjacent an inlet orifice to reduce the effects of wind on flow through the orifice, particularly in the presence of high winds such known bafl le means have permitted greater variations in the air flow through the orifice than are desirable for many purposes, and in the case of gas-fired heaters supplied with com- "ice bustion air through the orifice have resulted in lower thermal efficiency and greater frequency of pilot outage and/or flame instability than are desirable.

Accordingly, it is an object of the invention to provide a new and useful air baffle apparatus and system employing same.

Another object is to propide such an air baflle apparatus which is effective in reducing the effects of 'wind on air flow through an adjacent orifice.

A further object is to provide such apparatus which is effective in opposing the tendency for increased air flow into an adjacent orifice in response to high winds incident on said air baffle apparatus.

A further object is to provide such apparatus which is effective in maintaining more nearly constant the combustion-air flow to a gas burner by way of an orifice adjacent the baffle apparatus.

A still further object is to provide an improved sealedchamber type of gas-fired heater system in which a vent duct for flue gases passes upward to the atmosphere through the center of an opening in a top surface and the inlet orifice for combustion air is formed by the spacing between the exterior of the vent duct and the adjacent edges of said opening.

SUMMARY OF THE INVENTION These and other objects and features of the invention are achieved by the provision of air bafile apparatus which reduces the tendency for wind to increase the air flow and pressure at an orifice communicating with atmosphere, by deriving from the incident wind a counter air flow and applying it to oppose wind-induced increases in flow through the orifice.

More particularly, in accordance with the invention there are provided wall means having a surface which extends outwardly from an edge of the orifice, and main baffle means mounted adjacent one side of the orifice and extending transversely outwardly from the edge of the orifice over at least a part of the wall means, at a converging angle with respect to the wall means, thereby to provide a passageway for primary air flow between said wall means and the inner side of said baffle means. While such :a main baflle means by itself tends to mitigate to some extent the influences of wind on flow through the orifice, in accordance with the invention the effects of wind are further substantially reduced by providing the main baffle means with an apertured portion disposed outwardly of the edge of the orifice for enabling a secondary air flow into the primary-air passageway by way of the apertured portion in the main baffle means; this apertured portion cooperates with deflector baflle means extending along the inner side of the main baflle means so as to be impinged by the secondary air flow due to incident wind, the deflector baflle means being so angled and positioned as to deflect the secondary air flow downwardly toward the wall means, and in part backwardly and outwardly with respect to the edge of the orifice, thereby creating a force tending to oppose the windinduced increases in primary air flow and thereby maintaining more nearly constant the air flow and pressure at the orifice.

In the preferred embodiment, the orifice constitutes an annular region between the edges in an opening. in a horizontal top surface and the outer side of a vent conduit passing vertically upwardly through the center of the opening; the main baffle means is preferably in the form of an upright, generally frustoconical hood disposed about the vent conduit and above the orifice. The largerbase end of the hood is open and disposed downwardly and its upper end is sealed to the exterior of the vent pipe, the lower edge of the hood extending outwardly beyond the periphery of the orifice. The apertured portion of the hood extends around its circumference substantially in a horizontal plane, and the deflector baffle means preferably comprises a generally annular strip of material extending around the interior of the hood, adjacent but spaced inwardly from the apertured portion thereof, so as to be impinged by air passing through the apertured portion in response to incident wind and so as to deflect said air downwardly and outwardly. Preferably also, the deflector baflle strip has a substantially flat surface confronting the apertured portion of the hood and extending downwardly and outwardly at substantially 60:5" from the horizontal, and the lower edge of the deflector baffle strip preferably lies in substantially the same horizontal plane as the lower edge of the hood and is spaced horizontally from the adjacent edge of the orifice by at least about of its distance above said top surface. In one preferred form, the apertured portion of the hood comprises an array of holes through the hood, extending around the hood in a horizontal plane, and the deflector baflie strip is secured to the inside of the hood immediately above the array of holes.

While improvements in operation may be realized to some extent by utilizing less than all of the recited preferred features of the invention, the combination of all of these features in a single balfile apparatus has been found to provide best operation in opposing the effects of high winds.

BRIEF DESCRIPTION OF FIGURES Other objects and features of the invention will more readily be understood from a consideration of the following detailed description, taken in connection with the accompanying drawings, in which:

FIGURE 1 is a perspective View illustrating a preferred embodiment of air baflle means in accordance with the invention, as applied to a roof-top gas-fired heater unit;

FIGURE 2 is a graphical representation illustrating certain improved capabilities of the preferred embodiment of the invention in the presence of wind;

FIGURE 3 is a vertical section of a preferred embodiment of the baffle apparatus of the invention;

FIGURE 4 is a horizontal section, taken along lines 4-4 of FIGURE 3;

FIGURE 5 is an enlarged fragmentary section of the baflie apparatus shown in FIGURE 3, and illustrates the various flows of air and gases within the apparatus; and

FIGURE 6 is a graphical representation illustrating certain improvements in a balanced-flue gas-fired heater produced by use of one preferred form of the invention.

DETAHJED DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the particular preferred embodiment of the invention illustrated in the figures, which embodiment is shown and described merely by way of example and without in any way limiting the scope of the invention, FIGURE 1 shows a box-like housing 10 containing gas-fired heater apparatus of known form which is to be which is to be provided with venting to atmosphere for flue gases. The particular arrangement of gas-fired burner and heater system utilized within housing 10 may be conventional, and hence has not been shown.

Venting of flue gases from the gas heater to atmosphere is provided by way of the vertically-extending cylindrical pipe 12, which passes from below to above the top surface 14 of housing 10, through the center of a horizontal circular opening 16 in top surface 14. A conventional vent cap 18, which may take any of a number of different conventional forms, is positioned over the top of the vent pipe to protect it from rain and the like, and is provided with holes such as 20 in its side surfaces to permit easy efliux of the vented flue gases.

Combustion air for the gas-fired heater is supplied from atmosphere through the annular orifice 22 formed between the exterior of pipe 12 and the surrounding, outwardlyspaced edges of the opening 16. The air baflle apparatus of the invention is shown generally at 26, and comprises an annularly-apertured generally frustoconical hood 28 positioned above, and extending outwardly beyond, the edge of opening 16, together with deflector baflie means 30 positioned on ths inner side of hood 28 in a position to be impinged by wind blowing through the apertured portion of hood 28, as will be described in detail hereinafter.

Louvered openings such as 29 may be provided in various surfaces of the housing 10 to permit air-cooling of various motors and similar elements which may be utilized therein for the purpose of providing circulation of heated air or water from the heater to the building below. However, it will be understood that, in this embodiment of the invention, combustion-air supply for the gas-fired heater is solely by way of the annular orifice 22, the gas combustion chamber being sealed off from the louvered openings in the housing 10.

The unit shown in FIGURE 1 is assumed to be mounted on the top of the roof of a building, for example the flat roof of an office building, where it is exposed to a wide range of incident wind velocities. Such wind will tend to flow along the top surface 14 of the housing 10 and under the hood 28 to the combustion-air inlet orifice 22, thereby raising the pressure at, and the flow into, the latter orifice. The gas heater apparatus will normally be designed for optimum performance at zero or very low wind velocities, and if winds are permitted to affect substantially the pressure and air flow at orifice 22, the thermal efliciency of the heater may decrease very substantially and instability of the gas flame and/or outage of the pilot flame may occur, all of which are highly undesirable.

In the particular application of the invention illustrated in FIGURE 1, the air baflle apparatus is located near two adjacent edges of the housing 10, which edges tend to disturb the flow of incident wind in such manner that the characteristics of the air baffle apparatus are somewhat dependent upon the direction of arrival of the wind. In order to eliminate this variable, the entire bafile apparatus shown in FIGURE 1 was mounted for test purposes on a uniform top surface, and artificially-induced wind was applied along the top surface at various angles but under otherwise identical conditions. The same results were obtained for the various angles of incident wind, thus illustrating that the symmetrical physical arrangement of the baflle apparatus causes it to exhibit substantially omnidirectional characteristics in a horizontal plane. FIGURE 2 illustrates typical improvements found in such tests by the use of the baflie apparatus of the invention.

In FIGURE 2, ordinates represent static pressure in ten-thousandths of a p.s.i., measured at the inlet orifice 22, while abscissae represent incident wind velocity in miles per hour. Broken-line curve A in the figure illustrates the characteristic obtained when employing a hood generally similar in configuration to hood 28, having sides extending downwardly at an angle of about 23 from the horizontal, the hood however not being apertured, so that the operation in accordance with the invention was not obtained. The solid-line curve B shows the characteristic obtained when hood 28 was apertured and provided with the deflecting baflle means 30, in accordance with the invention.

It will be seen from FIGURE 2 that, for wind velocities up to about ten or twelve miles per hour, the static pressure at orifice 22 does not increase markedly with either type of baffle; however, with further increases in Wind velocity, particularly in the range from about 18 miles per hour upward, the inlet static pressure produced with the prior-art hood rises markedly, while when utilizing the 'hood of the invention and its novel deflecting baffle a much slower increase in inlet static pressure occurs with increases in wind velocity; this results in a smaller increase in the flow of combustion air into the gas-fired heater, and therefore in a smaller reduction in thermal efliciency and in frequency of flame instability or flame out.

Turning now to FIGURES 35 for a more detailed description of the construction and operation of the preferred embodiment of the invention, in which like parts are indicated by like numerals, the circular opening 16 in the top surface 14 of housing is in this exampleprovided with an upwardly-turned peripheral flange 34 for minimizing the possibility of the flow of rain water or other contaminants into the annular inlet orifice 22. The chamber 35 within housing 10 communicates with inlet orifice 22 and with the combustion chamber of the gas-fired heater in housing 10. Also, the lower end of cylindrical hollow vent pipe 12 communicates at its lower end (not shown) with the vent for flue gases from the gas-fired burner. While in no way limited thereto, the present apparatus will. be assumed to be of the type in which there i no forced draft of air, the inlet combustion air traveling inwardly to the gas heater in response to the chimney effect produced by the upward flow of vent gases through vent pipe 12. This flow ordinarily being of relatively low velocity, it will be appreciated that relatively small changes in absolute airvelocity due to wind may constitute a very substantial percentage change in the combustion-air flow.

The vent pipe 12 is held in an upright position by means (not shown) within housing 10, and the generally frustoconical hood 28 is positioned with its upper, smallerbase end soldered or otherwise aflixed tightly to the exterior of the vent pipe 12. An annular array of closelyspaced small holes such as 40 is provided in a common horizontal plane through the sloping sides of hood 28, thereby to provide the apertured portion 42 of the hood. The deflector baflle means 30, in the form of a flat annular metal strip, is secured to the inner side of hood 28 just above the array of holes 40, and is angled outwardly so that air flow through the apertures 40 due to wind will be deflected backwardly and downwardly to provide a secondary air flow opposing the primary air flow along the top surface 14 to inlet orifice 22.

Vertical strut supports 44 may also be provided at 120 intervals around the edge of the hood 28, these struts being secured at their lower ends to the top surface 14 of housing 10 to provide additional mechanical rigidity. Apertured vent cap 18 may be secured in position over the top of vent pipe 12 by soldering, or in any other convenient manner.

Referring now particularly to'FIGURE 5 for an explanation of the air flows involved and the significance of the various elements and their proportion and positions, the horizontal solid arrows in the latter figure represent incident wind arriving at the baflfle apparatus of the invention from the left; the open, unstippled arrows represent the primary air flow which occurs through the passageway formed by the top surface 14 and the undersurface of hood 28, into the inlet orifice 22. The vented flue gases are represented by the open, stippled, verticallyextending arrows.

The smaller solid arrows represent the secondary air flow produced primarily in response to the incident wind. This flow passes through the apertures 40 on the side of the hood impinged by the wind and, due to the presence of the opposed deflecting baflle means 30, turns down wardly and at least partially backwardly so as to produce a backward force which opposes the primary air flow and reduces its magnitude. Accordingly the flow of combustion air reaching inlet 22 in the presence of wind is substantially reduced, compared to that which would be obtained in the absence of the apertures 40 and the baflle means 30. The result is the desired mitigation of the effects of wind upon the combustion air flow.

Still with particular reference to FIGURE 5, the angle of the downwardly-converging slope of hood 28 is not critical, but should be sufficient to provide adequate frontal area for the secondary air holes 40 and a corresponding adequate secondary air flow in response to wind. As a practical matter, the angle of the hood is at least about 18 to the horizontal, and a 23 angle is preferred. The acute angle which the deflecting baffle strip 30 makes with the horizontal has been found to be more important in obtaining the indicated operation, and, for the case of a flat deflecting baflle strip of the type shown in the drawings, an angle of 60i5 to the horizontal is preferred for best results. Other significant dimensions are the spacing of the lower edge of the deflecting baflle strip 30 above the top surface 14, and the horizontal spacing of the lower edge of the deflecting baffle strip 30 from the edge of the inlet orifice 22. More particularly, it has been found that best results are obtained when the lower edge of deflecting bafifle strip 30 lies in substantially the same horizontal plane as the lower edge of the hood 28, and when the horizontal distance between the lower edge of deflecting baflle 30 and the edge of inlet orifice 22 is at least about of the vertical spacing between the lower edge of deflecting baffle 30 and the top surface 14.

In the operation of the baffle means of the invention, the forces introduced by the secondary air flow oppose wind-induced increases in primary air flow, and in addition the air flow to the inlet orifice 22 is further reduced by a reverse venturi effect due to the enlargement of the passageway between top surface 14 and hood 28 on the radially-inward side of deflecting baflle strip 30.

Without thereby in any way limiting the scope of the invention, the following specific detailed example of dimensions and construction is given in the interest of complete definiteness. In one embodiment of the invention the outer diameter of the vent pipe 12 was five inches, the diameter of the lower edge of the hood 28 was 16% inches and the slope of the hood sides was 23 to the horizontal. The diameter of the opening 16 on top surface 14 was seven inches, forming an annular inlet orifice 22 about two inches in width.

The holes 40 in this example consisted of 68 holes, W inch in diameter and spaced of an inch apart on their centers, the diameter of the circular array of holes, from center to center, being 12 inches. The deflector baflle strip was secured to the inner side of the hood 28 just above the array of secondary air holes and extended downwardly, at an angle of 60 to the horizontal, to a point lying in the same plane as the lower edge of hood 28. The height of the lower edge of hood 28 above the top surface 14 was two inches, and the height of the top of hood 28 above top surface 14 was 4% inches. The slant height of hood 28 was therefore about six inches, the centers of the secondary air holes being located 2% inches upward along the slanted surface of hood 28 from its lower edge. The diameter of the lower edge of the annular deflecting baflle strip was therefore about 12% inches. The lower edge of deflecting baffle strip 30 was spaced horizontally from the nearest edge of orifice 22 by 4 inch.

This specific form of apparatus, when tested as described above, produced the improved results illustrated and discussed hereinbefore in connection with FIGURE 2. FIGURE 6 is a graphical illustration of the improvement in thermal efliciency of a gas-fired heater obtained when used with the specific form of baffle apparatus just described, in the application illustrated in FIGURE 1; the baflle apparatus of the invention was located as shown in'FIGURE 1, and subjected to a wind blowing across the width dimension of the housing 10 from the side more remote from the baflle apparatus, as illustrated schematically in FIGURE 4.

More particularly, in the graph of FIGURE 6 ordinates represent percentage thermal efficiency of a balanced-flue gas-fired heater, while abscissae represent the incident wind velocity, in miles per hour, in the direction indicated. Curve A illustrates the drop-off in thermal efliciency with increasing wind velocity when utilizing baflle apparatus comprising a hood with 0 slope to the horizontal, and

containing no apertures therein; curve B represents the characteristic obtained with a hood having sides slanted at 23 to the horizontal, as in the preferred form of the present invention, but without secondary air holes so that that operation of the invention is not obtained; and curve C represents the characteristic obtained by the abovedescribed example of the present invention. It will be seen that, when utilizing the apparatus of the invention, the thermal efficiency remains well above 75% even for winds in excess of 25 miles per hour, while for the other structures the thermal efficiency drops well below 65%, and even below 60% in the case of curve A. Due to the non-symmetrical location of the baffle apparatus on the housing 10, the thermal efiiciency curves for other directions of wind will in general differ somewhat from that of FIGURE 6, but the net result is an improvement in over-all performance with respect to thermal efficiency.

It will be understood that the dimensions and construction specified in the detailed example above may be departed from substantially, while still realizing material advantages from use of the invention. For example, the, bafile need not be symmetrical or circular in form. Similarly, the hood 28 need not be frustoconical, the deflecting baflie means need not be flat, and the apertures in the hood need not be circular holes but may, for example, comprises thin elongated slits. The apparatus may also be scaled upwardly or downwardly from the dimensions indicated above, the ratio between the horizontal spacing of the lower edge of the deflecting baffle means 30 from the edge'of the inlet orifice 22, to the height of the lower edge of the deflecting bafiie means above the top surface, preferably remaining at a value of at least about /8 for best results.

Accordingly, while the invention has been described with particular reference to specific embodiments thereof in the interest of complete dcfiniteness, it will be understood that it can be embodied in any of a variety of forms widely diverse from those specifically shown and de-\ scribed, without departing from the scope of the invention as defined by the appended claims.

What is claimed is:

1. Air baflie apparatus for reducing the effects of wind on air flow through an orifice, comprising:

wall means having a surface extending outwardly from an edge of said orifice; main bathe means mounted adjacent one side of said orifice and extending transversely outwardly from said edge of said orifice and over at least a part of said wall means at a converging angle with respect to said wall means, thereby to provide a passageway for primary air flow between said wall means and the inner side of said main baflle means; i

said main baffle means having an apertured portion disposed outwardly of said edge of said orifice for enabling a secondary air flow into said passageway by way of said apertured portion; and

deflector baffle-means extending along the inner side of said apertured portion of said main bafiie means so as to be impinged by said secondary air flow in the presence of incident wind, and angled so as to deflect said secondary air flow downwardly toward said wall means and in part backwardly and outwardly with respect tosaidedge of said orifice, thereby to reduce the effects of wind on air flow through said passageway.

2. The apparatus of claim 1, in which said apertured portion of said main baflie means comprises a linear array of aperture means substantially equidistant from said surface of said wall means, and said deflector baflie means comprises a continuous strip of material extending adjacent the full length of said array.

3. The apparatus of claim 2, in which said strip extends in its width dimension from a position spaced from said surface by substantially the same distance as the converging edge of said main bafiie means, to a position on the inner side of said main baffle means beyond said array of apertures.

4. The apparatus of claim 1, in which said deflector baffle means r.m.s. an acute angle with said main baffle means and an angle of about 60- -5 with the subjacent portion of said surface of said Wall means.

5. The apparatus of claim 4, in which the edge of said deflector bafiie means adjacent said surface is spaced along said surface from said edge of said orifice by at least about of its spacing from said surface. I

'6. The apparatus of claim 1, in which said apertured portion of said main bafiie means and said deflector bafiie means both circumscribe said orifice.

7. Air bafiie apparatus comprising:

wall means having a substantially horizontal upper surface provided with an opening extending therethrough;

a member extending substantially vertically through the center of said opening and spaced inwardly from the sides thereof, thereby to define an air flow orifice between said member and the surrounding edges of said opening;

main baflle means comprising a hood surrounding said member and having downwardly and outwardly sloping side surfaces, the lower edge of said hood lying substantiallyin a horizontal plane and extending radially outward beyond said orifice, an upper portion of said hood closely encompassing the exterior surfaces of said member, said wall means and said hood providing between them a passageway for primary air flow between said orifice and the exterior;

said hood having an apertured portion extending around it substantially in a horizontal plane, thereby to enable a secondary air flow into said passageway from the exterior side of said hood; and

a deflecting baffle extending around the interior of said hood in the plane of said apertured portion thereof and spaced inwardly therefrom, so as to be impinged by secondary air flowing inwardly through said apertured portion of said hood in response to incident wind, for directing said secondary air flow downwardly and outwardly;

the lower edge of said deflecting baflie lying substantially in said plane of said lower edge of said hood, the upper edge of said deflecting bafiie being sealed to the inner side of said hood around the interior thereof above said apertured portion thereof;

said lower edge of said deflecting baffle means being horizontally spaced from the outer edge of said orifice by at least about of its vertical spacing from said wall means.

8. The apparatus of claim 7, in which said deflector baffle means comprises a flat strip of material the width dimension of which extends downwardly and outwardly at substantially 60i5 to the horizontal.

9. The apparatus of claim 7, in which said apertured portion of said hood comprises a plurality of holes spaced from each other around said hood.

10. The apparatus of claim 7, in which said member comprises a hollow conduit open at its upper end.

11. Baffle apparatus for reducing the elfects of wind on air flow into a gas-fired heater of the type having a horizontal top surface, having an air outlet communicating with an upright vent pipe extending through the center portion of an opening in said top surface, and having an air inlet communicating with the orifice provided by the space between said vent pipe and the edges of said opening, said apparatus comprising:

an upright generally frustoconical hood disposed about said vent pipe and above said orifice, said hood having its larger-base end open and disposed doWn wardly and its upper end sealed to the exterior of said vent pipe, the lower edge of said hood extending outwardly beyond the periphery of said orifice;

said hood having a generally annular apertured portion extending around its circumference substantially in a horizontal plane; and

deflector bafile means comprising a generally circular strip of material extending around the interior of said hood, adjacent but spaced inwardly from said apertured portion thereof, so as to be impinged by air passing through said apertured portion in response to incident wind and to deflect said air downwardly and outwardly;

said strip having a substantially flat surface confronting said apertured portion of said hood and extending downwardly and outwardly at substantially 60 -5 from the horizontal;

the lower edge of said strip lying in substantially the same horizontal plane as the lower edge of said hood, and being spaced horizontally from the edge of said orifice by at least about of its distance above said top surface.

12. The apparatus of claim 11, in which said aper- References Cited UNITED STATES PATENTS 2,701,999 2/1955 Moran 98- -58 3,221,730 12/1965 Hughes, et al 126307 WILLIAM E. WAYNER, Primary Examiner US. Cl. X.R.

" UNITED STATES PATLNT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,490,352 Dated January 20, I970 Inventor(s) Richard M. Oehlschlaeger It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

r ff Column 1, line 15, "communcating" should read --communicating Column 3, line ll, "60" should read --60-. Column 3, line 57, after the word "be" insert --suppl1ed from atmosphere with combustion air, and--. Column 4, line 5, 'ths" should read --the--. Column 7, line 5, "that" should read --the--. Column 7, Line 26, "comprises" should read "com rise". Column 8, line 4, "r.m.s." should read --forms--. Column 8, line 67, insert --baffle before "apparatus SIGNED AND SEMI?!) AUG 251973 (SEAL) Atteat:

Edward Fletch,

u. I. mm! 1. W. m- S Oomissiom at Ma 

